Semiconductor memory device

Abstract

This semiconductor memory device comprises: a memory cell array configured as an arrangement of memory cells disposed at intersections of a plurality of first lines disposed substantially in parallel and a plurality of second lines disposed to intersect the first lines, each of the memory cells including a variable resistance element; and a control circuit configured to control the memory cell array. The control circuit is configured to change a voltage value of a resetting verify voltage applied for confirming completion of the resetting operation according to a degree of change of resistance of the memory cell when performing the resetting operation to change the memory cell from a low-resistance state to a high-resistance state.

What is claimed is: 
     
       1. A semiconductor memory device, comprising:
 a memory cell array configured as an arrangement of memory cells disposed at intersections of a plurality of first lines disposed substantially in parallel and a plurality of second lines disposed to intersect the first lines, each of the memory cells including a variable resistance element; and 
 a control circuit configured to control the memory cell array, 
 the control circuit being configured to change a voltage value of a resetting verify voltage applied for confirming completion of a resetting mode according to a degree of change of resistance of the memory cell when performing the resetting operation to change the memory cell from a low-resistance state to a high-resistance state. 
 
     
     
       2. The semiconductor memory device according to  claim 1 , wherein
 the control circuit is configured capable of executing a judgment mode for judging the degree of change of resistance of the memory cell in the resetting operation, in addition to the resetting mode, and 
 the control circuit changes the voltage value of the resetting verify voltage based on a judgment result of the judgment mode. 
 
     
     
       3. The semiconductor memory device according to  claim 2 , wherein
 the judgment mode executes the resetting operation on a first memory cell group in the memory cell array, and judges the degree of change of resistance of the memory cell based on the number of memory cells in the first memory cell group that have changed to a first resistance state. 
 
     
     
       4. The semiconductor memory device according to  claim 3 , wherein
 before the resetting operation on the first memory cell group, the judgment mode executes on the first memory cell group a setting operation to change the memory cell from the high-resistance state to the low-resistance state. 
 
     
     
       5. The semiconductor memory device according to  claim 3 , wherein
 the plurality of second lines are each connected to a row decoder, and the first memory cell group is selected from the memory cells connected to a single one of the plurality of second lines. 
 
     
     
       6. The semiconductor memory device according to  claim 3 , wherein
 the plurality of first lines are each connected to a sense amplifier, and the first memory cell group is selected one each from the memory cells connected to a single one of the plurality of first lines. 
 
     
     
       7. The semiconductor memory device according to  claim 1 , wherein
 the control circuit changes a voltage value of a setting verify voltage applied for confirming completion of a setting operation when the setting operation is performed, according to the degree of change of resistance of the memory cell when performing the resetting operation. 
 
     
     
       8. The semiconductor memory device according to  claim 7 , wherein
 the control circuit is configured capable of executing a judgment mode for judging the degree of change of resistance of the memory cell in the resetting operation, in addition to the resetting mode, and 
 the control circuit changes the voltage value of the resetting verify voltage based on a judgment result of the judgment mode. 
 
     
     
       9. The semiconductor memory device according to  claim 8 , wherein
 the judgment mode executes the resetting operation on a first memory cell group in the memory cell array, and judges the degree of change of resistance of the memory cell based on the number of memory cells in the first memory cell group that have changed to a first resistance state. 
 
     
     
       10. The semiconductor memory device according to  claim 9 , wherein
 before the resetting operation on the first memory cell group, the judgment mode executes on the first memory cell group a setting operation to change the memory cell from the high-resistance state to the low-resistance state. 
 
     
     
       11. The semiconductor memory device according to  claim 9 , wherein
 the plurality of second lines are each connected to a row decoder, and the first memory cell group is selected from the memory cells connected to a single one of the plurality of second lines. 
 
     
     
       12. The semiconductor memory device according to  claim 9 , wherein
 the plurality of first lines are each connected to a sense amplifier, and the first memory cell group is selected such that a single memory cell is selected from among the memory cells connected to single one of the plurality of first lines. 
 
     
     
       13. A method of controlling a semiconductor memory device, the semiconductor memory device including a memory cell array configured as an arrangement of memory cells disposed at intersections of a plurality of first lines disposed substantially in parallel and a plurality of second lines disposed to intersect the first lines and each including a variable resistance element, the method comprising:
 judging a degree of change of resistance of the memory cell when performing a resetting operation to change the memory cell from a low-resistance state to a high-resistance state; and 
 changing a voltage value of a resetting verify voltage applied for confirming completion of a resetting mode, according to a result of the judgment. 
 
     
     
       14. The method of controlling a semiconductor memory device according to  claim 13 , wherein
 the judgment executes the resetting operation on a first memory cell group in the memory cell array, and judges the degree of change of resistance of the memory cell based on the number of memory cells in the first memory cell group that have changed to a first resistance state. 
 
     
     
       15. The method of controlling a semiconductor memory device according to  claim 14 , wherein
 prior to the resetting operation on the first memory cell group, the judgment executes on the first memory cell group a setting operation to change the memory cell from the high-resistance state to the low-resistance state. 
 
     
     
       16. The method of controlling a semiconductor memory device according to  claim 15 , wherein
 the voltage value of a setting verify voltage applied for confirming completion of the setting mode is changed according to the degree of change of resistance of the memory cell when performing the resetting operation. 
 
     
     
       17. The method of controlling a semiconductor memory device according to  claim 14 , wherein
 the plurality of second lines are each connected to a row decoder, and the first memory cell group is selected from the memory cells connected to a single one of the plurality of second lines. 
 
     
     
       18. The method of controlling a semiconductor memory device according to  claim 14 , wherein
 the plurality of first lines are each connected to a sense amplifier, and the first memory cell group is selected such that a single memory cell is selected from among the all memory cells connected to single one of the plurality of first lines.